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The feature that would make RB complete is IR transceiver support. Unfortunately there does not seem to be to many options out there for IR hardware that is affordable. Last night I found a $40 USB IR transceiver that can send and receive IR available from http://iguanaworks.net/.
They have GPL source to control the device and there is a free OS X control panel from another developer that that records IR codes from your remote and can IR blast them or listen for them and execute appelscript when it receives an IR code. It should work with RB through applescript, but native support for the IguanaWorks transceiver would be much faster and easier to set up.
I hope Felix will look at the hardware and source and consider adding it to RB. It would be really great!
I am going to order one and see how well it works with RB and applescript but I don't expect to volume control of my AV receiver to work very well. At least on/off should work. I always forget to turn it off. I already have RB set up to turn on/off my lights (insteon) when I launch/quit PLEX. I am going to add on/off for my AV receiver with one of these IR transceivers.